Fitting a GFB Respons BOV Dump Valve

A controversial topic now – dump valves. Or BOV’s, VTA’s, whatever you want to call them. Regardless, I’ve fitted one to my STi.

I was always a little heartbroken to discover that upon purchasing my Subaru, the fitment of a dump valve is not recommended in any way on a standard car. The WRX/STi models run a full recirculation system with a MAF sensor, so air is not and should not be dumped out of the system, but rather recirculated back in (as it has been measured by the MAF and fueling has been adjusted accordingly).

You can read online for hours and hours about the pros and (mostly) cons of fitting a VTA valve, but ultimately only you know what you want to do. And for me at least, I wanted more noises!

I couldn’t find a single example of any actual ‘damage’ being done to an engine solely from fitting a BOV, just murmurs of slightly decreased performance, so I swallowed a brave pill and took a chance.

I decided to go for a GFB Respons T9003 BOV, which is more of ‘hybrid’ BOV in that it can either 100% VTA (vent to atmosphere) or 100% recirculate with a simple twist of a dial. You can set the bias any way in between too to adjust the noise. Very cool.

Made by an Australian company called Go Fast Bits, it looks like a very well put together bit of kit. It comes with some nice packaging, decent fitting instructions, hardware and an allen key for spring adjustment. You can read all about this particular model for a newage WRX/STi (the GFB T9003) here.

I found mine from a supplier on eBay here for around £200 after discounts, but any reputable Subaru parts specialist would be able to source one, for example here and here.

BOV’s are just bolt-on items, so fitment was fairly straightforward, if a little awkward due to the lack of space available (as I didn’t want to remove my TMIC).

There are just two bolts holding the original recirculating valve in place, and a couple of hoses. I had to wrestle the hose off going to the original valve as it seemed to semi-weld itself to it. But some grazed knuckles and a bit of swearing later, it was off.

You’ll want to remove the elbow piece from your original valve and attach it to the GFB too, but this is all explained in the provided instructions.

Looks smart and stealthy once fitted:

After a few trial runs dialling the spring tension in, and adjusting the bias valve to a noise level I’m happy with, I’m really pleased with the GFB Respons.

I didn’t want a shouty, deafening BOV noise – rather just a subtle hint that there’s something there. And this is exactly what I’ve set it to, with something like a 10% VTA, 90% recirc.

Best of all I just love having the options. If I’m sick of the VTA noises I can simply shut it off to 100% recirc. If I’m feeling like a spirited drive, I can set the VTA to a greater percentage and revel in the noises.

One thing I will mention is that upon fitment it seems to have induced some very mild open-throttle compressor surge. I’ve managed to eliminate most of this with the spring tension adjustment, but there’s still a little remaining and I’m not really sure what else I can do about it. Any commentators want to let me know what this could be?

Overall, I’m really happy. It doesn’t seem to have changed the car’s performance at all (better or worse), but at least now my STi is making all the right noises!

Let me know if you want to see a video in the comments below, and I’ll try to arrange something.

About The Author

Hi, I'm Jay. Thanks for stopping by! If you have any questions or anything to say, please feel free to let me know in the comments on any post - I'll be happy to respond. Find me on Instagram or read more about my Subaru Impreza at any time :)